1. Field of the Invention
The present invention relates to a toothbrush.
2. Description of the Related Art
Various kinds of manners for cleaning teeth by a toothbrush have been suggested so far, and, above all, a so-called Bass or scrub method, in which bristles of a toothbrush are substantially reciprocated in the axial direction of the main body of the toothbrush at a short stroke of several millimeters, has been recently recognized to be the most effective in removing plaque. However, a pressure at which an ordinary person presses the bristles against teeth is approximately 300-500 g. In this case, the bristles of an ordinary toothbrush curl up at the ends, and it is difficult for the distal ends of the bristles to reach a portion between teeth or between teeth and gums where the plaque is apt to collect. Even if the ends of the bristles reach there, since they curl up, a satisfactory brushing effect cannot be obtained. As a result, it is not expected that the plaque will be removed by reciprocating the toothbrush at a short stroke. Furthermore, if the teeth are brushed under such a great pressure, the gums regress, and the surfaces of the teeth are worn out, this resulting into a wedge-shaped defect. Accordingly, the optimum pressure of the bristles is approximately 70-200 g. When the Bass or scrub method is carried out at this pressure, the ends of bristles reach a portion between the teeth and between the teeth and the gums where plaque causing pyorrhea, such as anaerobic bacteria, is most apt to collect. Since the plaque is stirred by the bristles, oxygen is supplied to the plaque, thereby controlling the increase of the plaque. In addition, a wedge-shaped defect and so on can be prevented.
Thus, in order to obtain a satisfactory brushing effect on teeth, while it is necessary to pay attention to the manner or direction of movement of the hand, it is very important to optimize the pressure of bristles of the toothbrush against teeth or the like. However, no well-known type of brush takes the brushing at the optimum pressure into consideration.
On the other hand, electrically driven toothbrushes each of which performs brushing by using an electric motor have been recently developed. Electrically driven toothbrushes disclosed in, for example, Japanese Patent Laid-Open Publication Nos. 57-166108, 58-69505 and 58-105709 and Japanese Patent Post-Examination Publication No. 42-27372 each substantially reciprocate the ends of bristles in the axial direction of a head portion at a short stroke of several millimeters. Furthermore, Japanese Patent Laid-Open Publication Nos. 59-40807 and 57-69806 disclose the reciprocal rotation of the ends of bristles around an axis of a head portion.
Such electrically driven toothbrushes are convenient to the user since he does not need to move his hand, while he becomes less attentive to brushing. In particular, the user is apt to be careless about the optimum pressure of bristles against teeth, and to inadvertently press the ends of the bristles of a reciprocating toothbrush against the teeth strongly, this causing damage to gums.
Furthermore, in the above conventional electrically driven toothbrushes, if bristles are pressed against the teeth with a relatively strong force in order to brush the teeth strongly, the load acting on a motor is increased, the rotation torque of the motor is decreased, and the reciprocation of the bristles is decelerated, and therefore, desired strong brushing cannot be achieved.
It is said that the stroke of the above linear or rotational reciprocation should be changed in accordance with a portion to be actually brushed. For example, in order to brush the surfaces of teeth or give a massage to gums, it is preferable that the reciprocation stroke be relatively large. To the contrary, when a narrow portion, for example, a portion between teeth, an occluding portion of teeth, or a boundary between teeth and gums, is brushed, the reciprocation stroke should be small. However, the above conventional electrically driven toothbrush cannot change the reciprocation stroke. Therefore, it is necessary to prepare a plurality of electrically driven toothbrushes having different reciprocation strokes in order to perform proper brushing depending on a portion to be brushed. Although it can be thought to use a motor serving as a drive source which can rotate in the normal and reverse directions, and to operate an electric switch so as to, for example, select a small reciprocation stroke in the normal rotation or a large reciprocation stroke in the reverse direction, the use of such an electric selection switch complicates the structure of the toothbrush, increases the cost, and causes trouble. Furthermore, it has been proposed that an intermediate transmission member for converting a rotational movement of a motor into a reciprocal movement and transmitting the reciprocal movement to a brush head is made to be tiltable from a reference position and the reciprocation stroke of the brush head is changed in accordance with the tilting distance of the intermediate transmission member (see, for example, U.S. Pat. No. 4,326,314). In this case, the structure of the toothbrush is complicated, the driving force transmission mechanism is apt to be broken down, and it is feared that a problem in sealing with respect to water will arise since the intermediate transmission member itself tilts.